Write on the back of your photos by following these guidelines from the National Archives. You won't damage your photos, and it will document the events, dates, or people in your pictures, and preserve the information for years to come.
Recently, a boy I once knew died a tragic death in a far away land. Of course, the boy I actually knew was gone decades ago, replaced by a 52 year old man that I hadn’t seen since high school and whose picture I barely recognized. But for me, the person lost with his 
death was the tallest and best looking member of my 1970 swim team. And so, the day I got the news, drowning in memories of my youth, I pulled out this photo taken in the summer before my 8th grade year.
For most of my childhood my neighborhood pool was the center of my summer life. We started every day with an early morning team practice, and after giving up the pool to the little kids’ lessons we raced back at 1:00 and stayed until closing at 6:00. We spent our afternoons playing Marco Polo in the pool and baking in the Arizona sun, before the days of SPF 30. Every one of the 57 kids in this photograph lived within a couple miles of my house and attended the same public schools I did.
What a shock and disappointment then to find that I could only name about ten of them. And then what a thrill to pull the photo off the sticky photo album page (more on those pages another time) and turn it over to find this, a complete listing of the team, in my own 12-year-old printing. A gift of precious information from my pre-adolescent self to my post-menopausal one.
Luckily enough, I had unwittingly done exactly what the preservation experts at the National Archives suggest, i.e. writing on the back of your photo with that old stand-by, a soft lead pencil. Pencil will not harm photos, won’t run or smear and works like a charm on most old photos. Newer photos can be trickier; most modern photo paper does not work well with pencil or most inks. For these photos, felt tip film marking pens are suggested – but be careful to let the ink dry completely before stacking photos. For tons of suggestions on how to preserve your family archives, visit the website of The National Archives.
http://www.archives.gov/preservation/family-archives/captioning-photos.html
- Kristi Woodworth